She shared this year’s chemistry Nobel — worth close to $1 million — with George P. Smith, 77, and Gregory P. Winter, 67. Dr. Arnold received half of the prize, and Dr. Smith and Dr. Winter split the other half.

Dr. Arnold won for her work conducting the directed evolution of enzymes, proteins that catalyze chemical reactions. She first pioneered the bioengineering method, which works similar to the way dog breeders mate specific dogs to bring out desired traits, in the early 1990s, and has refined it since then.

Her enzymes have been used to make biofuels, medicines and laundry detergent, among other things. In many processes, they have taken the place of toxic chemicals.

Dr. Smith was honored for developing a method, known as phage display, in which a virus that infects bacteria can be used to evolve new proteins. Dr. Winter won for evolving antibodies through phage display to combat autoimmune diseases and in some cases, cure metastatic cancer.

“I think of what I do as copying nature’s design process,” Dr. Arnold said in an interview with NobelPrize.org. “All this tremendous beauty and complexity of the biological world all comes about to this one simple beautiful design algorithm.”

In the 1980s, Dr. Arnold tried to rebuild enzymes, but because they are very complex molecules built from different amino acids that can be infinitely combined, she found it difficult to remodel the enzymes’ genes in order to give them new properties.

In the 1990s, she abandoned what she called her “somewhat arrogant approach” of trying to create modified enzymes through her logic and knowledge, and examined nature’s way of doing things. She looked into evolution.

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Dr. Arnold with President Barack Obama at an award ceremony for the National Medal of Technology and Innovation in 2013. Dr. Arnold was awarded the prize in 2011.CreditBrendan Hoffman/Getty Images

“I realized that the way most people were going about protein engineering was doomed failure,” Dr. Arnold said. “To me it is obvious that this is the way it should be done.”

She tried to change an enzyme called subtilisin. She wanted it to accelerate change in an organic solvent, so she created random mutations in the enzyme’s genetic code and introduced the mutated genes to bacteria that then created different types of subtilisin.

Dr. Arnold selected the type of subtilisin that performed the best. Once she found the best variant of subtilisin, she continued to mutate it until she had the very best version.

With this directed evolution, she could show the power behind allowing chance and directed selection instead of depending on human logic and understanding of how genes and enzymes are supposed to work. This was the initial step toward the revolution in enzyme mutation.

When she began her new approach, “some people looked down their noses at it,” Dr. Arnold told the National Science and Technology Medals Foundation. “They might say ‘It’s not science’ or that ‘Gentlemen don’t do random mutagenesis.’ But I’m not a scientist, and I’m not a gentleman, so it didn’t bother me at all. I laughed all the way to the bank, because it works.”

Now, Dr. Arnold said, these are some of the questions she would like to answer: “How do you evolve innovation? How do you get a whole new chemical activity that you don’t know already existed? How can I evolve a whole new species of enzymes?”

Dr. Arnold was born on July 25, 1956, in Pittsburgh. In 1979 she received her undergraduate degree in mechanical and aerospace engineering from Princeton University. She received her graduate degree in chemical engineering from the University of California, Berkeley, in 1985.